Drilling rig floor structure



March 3, 1970 G. D. KNORR 3,498,392

DRILLING RIG FLOOR STRUCTURE Filed June 7. 1968 8 Sheets-Sheet 1 INVENTOR. 60220 flw mv 16/022 March 3, 1970 s. o. KNORR 3, 9

DRILLING RIG FLOOR STRUCTURE Filed June '7, 1968 8 Sheets-Sheet 2 MIME/V7016 3% I 6020M m/mA/rje March 3, 1970 e. D. KNORR 3,

DRILLING RIG FLOOR STRUCTURE Filed June 7. 1968 8 Sheets-Sheet 5 INVENTOR. 6020M DAmv/v 161/0 March 3, 1970 s. 0. KNORR 3,

DRILLING RIG FLOOR STRUCTURE Filed June '7, 1968 8 Sheets-Sheet 4 I N VEN TOR. 6050M .DAV/JA/ 164/022 w mk March 3, 1970 cs. D. KNORR DRILLING RIG FLOOR STRUCTURE 8 Sheets-Sheet 5 Filed June 7, 1968 March 3, 1970 a. D. KNORR 3,

DRILLING RIG FLOOR STRUCTURE March 3, 1970 G. D. KNORR 3,498,392

DRILLING RIG FLOOR STRUCTURE Filed June 7. 1968 8 Sheets-Sheet 7 I N VEN TOR. 60500 24/70 Maze wazl/ March 3, 1970 G.,D. KNORR DRILLING RIG moon smnucmm 8 Sheets-Sheet 8 Filed June 7. 1968 E .e 1 \w a kw s M Q mmwm A v fi w U Q h m m M o fiv J 6 w WQNMMQ United States Patent 3,498,392 DRILLING RIG FLOOR STRUCTURE Gordon Dayton Knorr, Long Beach, Calif., assignor to Global Marine Inc., Los Angeles, Calif., a corporafiOn of Delaware Filed June 7, 1968, Ser. No. 735,365 Int. Cl. E21b 7/12, /02; E21c 19/00 US. Cl. 175-5 22 Claims ABSTRACT OF THE DISCLOSURE A drilling rig floor structure, especially useful in offshore drilling installations, in which a power operated hinged door extends from an edge of the floor to a rotary table which is retractably mounted in the center of the floor. Hinging of the door and retraction of the rotary table relative to the stationary portion of the floor provides an access passage from the side to the center of the floor through which may be moved a blowout preventer stack or the like.

BACKGROUND OF THE INVENTION Field of the invention This invention pertains to a power operated, openable floor structure for drilling rigs, particularly drilling rigs supported on floating vessels.

Review of the prior art The utility of this invention is believed to be greatest in, but is not limited to, the context of floating drilling vessels. For this reason, this invention is described herein in the environment of a floating drilling vessel, and the prior art considered pertinent to the invention is reviewed with respect to such an environment. Basically, floating drilling vessels comprise a drilling rig mounted to the main deck of a ship of conventional hull form. The shipmounted drilling rig is as similar as possible to land-based drilling rigs.

The basic purpose of such a floating drilling vessel is to carry out oil exploration and production operations with equipment which often is designed for use primarily in corresponding land-based procedures. The considerations pertaining to the basic purpose of the vessel are important technical and economic aspects of drilling ship design and often are sharply at odds with optimum naval architectural and marine engineering design parameters which include vessel stability.

The stability of a floating vessel of conventional hull form is directly related to the proximity of the vessel center of gravity to the keel. While the center of gravity may be, and usually is located higher from the keel than the vessel center of buoyancy, the amount by which the center of gravity may be higher than the center of buoyancy is limited. Of course, the center of gravity of the entire vessel may be lowered from the center of gravity of the basic vessel structure by the use of ballast carried low in the vessel, but the extensive use of ballast is not favored since such practices reduce the useful equipment and supply carrying capacity of the vessel.

The drilling rig carried by a floating drilling vessel includes a rig floor structure supported above the vessel main deck over a well vertically through the center of the ship, and a derrick erected over the rig floor. This structure is relatively massive and its presence has a significant effect upon the vertical position of the vessel center of gravity.

It has been found that it is impractical and inefiicient to locate the rig floor directly upon the vessel main deck because of the necessity, at various times during offshore 3,498,392 Patented Mar. 3, 1970 .r' CC drilling operations, to move various pieces of equipment, notably blowout preventer stacks, into position below a rotary table carried in the rig floor over the vessel center well. Thus, elevating the drilling rig above the vessel main deck further raises the vessel center of gravity and reduces vessel stability. For these reasons, the amount of rig floor elevation above the vessel main deck must be kept as small as possible, consistent with the basic purposes for which the vessel is designed. The practice in the past has been to elevate the rig floor sufliciently to enable the passage, under the rig floor along the vessel main deck to over the center well, of most previously used blowout preventer stacks; this practice places the rig floor at such a height that the vessel center of gravity is located so as to provide almost the minimum safe margin of stability for the vessel. This design compromise, necessitated by the marriage of a drilling rig to a ship, presents operational problems in the drilling of large diameter submarine oil wells and in the drilling of wells in water depths not previously encountered.

As the size of the drilled well increases, or as wells are drilled in increasingly large depths of water, the size of the equipment needed in the drilling process increases. The piece of equipment involved in the problem to which this invention is addressed is the blowout preventer stack used to controllably close the drill hole in the event that gas or oil at high pressures is unexpectedly encountered as the well is drilled. Blowout preventer stacks for large diameter wells and for deep water wells are too high to pass below the rig floors of drilling rigs mounted to vessel hulls of economical and practical dimension and form; this is the problem, and its significance is being felt more and more as larger and larger wells are being drilled in greater and greater water depths.

For the reasons given above, the problem cannot be solved merely by further elevating the drilling rig floor above the vessel main deck. While the dimensions or form, or both, of the vessel could be altered to produce a beneficial effect upon the relation between the vessel center of buoyancy and the vessel center of gravity, such a solution is obviously not practical with respect to existing vessels and usually is not economically realistic with respect to vessels yet to be constructed specially for offshore drilling operations.

SUMMARY OF THE INVENTION Briefly, this invention provides a drilling rig which includes an elevated floor and a rotary table mounted in the floor at a normal operational position disposed centrally of the side edges of the floor. The floor has a major stationary portion, and includes door means hinged to the stationary portion. The floor door means extend from the operational position of the rotary table to a side edge of the floor. Power means are connected to the door means for hingably moving the door means relative to the floor stationary portion to provide an access passage from the floor side edge to the operational position of the rotary table. The structure of the invention also includes means for moving the rotary table from its operational position to provide an extension of the access passage to centrally of the floor.

As noted above, the present invention is believed to have its greatest utility when incorporated into the structure of a floating drilling vessel. It will be understood, however, that the invention can be used to advantage in other drilling structures, as in non-floating offshore drilling installations and facilities, for example.

DESCRIPTION OF THE DRAWINGS The above-mentioned and other features of the invention are more fully set forth in the following detailed description of a presently preferred embodiment of the structure and operation thereof, which description is presented with reference to the accompanying drawings, wherein:

FIG. 1 is a fragmentary side elevation view of the base of a drilling rig on a floating drilling vessel showing a large blowout preventer stack stored adjacent the rig;

FIG. 2 is a top plan view of the floor of the drilling rig shown in FIG. 1;

FIG. 3 is a fragmentary plan view of the substructure of the rig fioor shown in FIG. 2;

FIG. 4 is an enlarged plan view of a portion of the structure shown in FIG. 3;

FIG. 5 is an enlarged elevation view taken along line 55 in FIG. 4;

FIG. 6 is a top plan view of the supporting base for the drilling rig and to which the structure shown in FIG. =3 is mounted;

FIG. 7 is an elevation view taken along line 7-7 in FIG. 6.

FIG. 8 is a side elevation view of the rotary table and its supporting sled;

FIG. 9 is a top plan view of the structure shown in FIG. 8 and of a sled hold-down device mounted to the structure shown in FIG. 6;

FIG. 10 is a fragmentary plan view of the rotary table sled drive means;

FIG. 11 is an enlarged elevation view taken along line 1111 in FIG. 9;

FIG. 12 is an elevation view of a portion of the sled drive means; and

FIG. 13 is a cross-sectional elevation view of the sled guide structure.

DESCRIPTION OF THE PREFERRED EMBODIMENT A floating drilling vessel 10 (see FIG. 1) has a hull 11 having a main deck ;12. A center well 13 is formed vertically through the hull at about midships of the vessel. A drilling rig 14 is erected on the hull over the center well and includes a rig floor structure 15, a truss-work foundation 16 supporting the floor structure above the main deck over the center well, and a derrick 17 supported on the foundation. Most drilling operations are carried out on the floor of the drilling rig, although some operations, especially operations peculiar to offshore drilling, are carried out on the main deck and in the center well.

In drilling an oil well from a floating drilling vessel, a conductor pipe is run down from the vessel through the center well to the ocean bottom and is either jetted or drilled into the ocean bottom to establish a connection between the vessel and the geology of the ocean bottom. A landing base is then lowered on cables along the conductor pipe into contact with the ocean bottom, the cables thereafter serving as guides for the movement of additional pieces of equipment between the vessel and the hole. A string of drill pipe and a drilling tool are then run from the rig through a rotary table 18 (see FIG. 2) mounted in the rig floor, through the conductor pipe and into the ocean floor, and the hole is drilled out for a short distance. Suitable casing is next inserted into the hole and is cemented to the geology to permanently establish the upper end of the well, the landing base forming a part of the permanent structure on the ocean floor.

Upon completion of the foregoing procedures, and before drilling is actually commenced in earnest, a blowout preventer (BOP) stack 19 (see FIG. 1) is installed on the landing base. To install the BOP stack, all drill pipe and conductor pipe is run up from the well. The BOP stack is moved along the vessel main deck into position over the center well, and is then lowered along the' guide cables by a string of drill pipe into proper registry with the landing base. After the BOP stack has been properly seated on the wellhead at the landing base, a drilling mud riser pipe is connected between the vessel and the stack. Drilling then may be commenced in earnest.

As shown in FIG. 1, BOP stack 19 normally is stored on the vessel main deck on a wheeled dolly 20 engaged with rails 21 which extend from the position in which the stack is stored to the adjacent edge of the center well. Previously, where small sizes of drill pipe and oil conductor pipe were used in conjunction with relatively small diameter holes, the BOP was sufliciently small that it could be stored under the rig floor on the vessel main deck. Today, however, wells are being drilled in greater and greater depths of water, and the economics of such activities encourages the drilling of wells of larger and larger diameter. Ideally, larger and larger BOP stack-s should :be used for safety and adequate control over the wells during the drilling procedure. Wellhead diameters of 16%" and more are becoming increasingly common.

FIG. 1 illustrates the problem presented by a BOP stack for use with a 16%" wellhead; stack 19 is constructed for use with such a wellhead and, with its supporting dolly, extends approximately 26 feet above main deck 12. The top of foundation 16 is located about 23 feet above the main deck. Obviously, stack 19 could not merely be run along the rails to the center well were floor structure 15 and foundation 16 of conventional design.

As shown in FIGS. 1 and 6, drilling rig foundation 16 includes a forward thwartships arch 23, and port and starboard arches 24 and 25, each of which extends continuously along a corresponding side of the foundation as shown in FIG. 1 relative to starboard arch 25. The rear side of the foundation, however, is defined by a pair of column-like half-arches 2-6 and 26' having inboard extremities 27 and 27' which are spaced from each other a distance at least as great as the thwartships width of BOP stack 19 which has its storage position aft of the drilling rig as shown in FIG. 1. Parallel box beams 28 and 28' connect the inboard extremities of the half-arches with the forward arch (see FIG. 6) and define the sides of an opening 29 in the foundation, the opening extending more than half the distance from the rear side of the foundation to the front side thereof. Fore-and-aft girders 30 and transverse girders 31 laid over the box beams and arches further comprise the horizontal part of the foundation upon which floor structure 15 is constructed. A support pad 3-2 for a leg of the derrick is located at each upper corner of the foundation.

The arrangement of rig floor 15, and of certain pieces of equipment mounted thereon, is shown in FIG. 2. Rotary table 18, when in use, is located centrally of the forward 34, port 35, starboard 3-6 and aft 37 edges of the floor. A derrick drawworks 38-is located along the starboard edge of the floor. Skate rails 39 of a drill pipe handling and racking assembly extend from the forward edge of the floor to a mouse hole 40 (in which a joint of drill pipe may be stored temporarily) located in a removable floor section 41 just forward of the rotary table. The skate rails are severableover the forward edge of floor section 41. A rathole 42, in which a kelly joint may be stored, is located between floor section 41 and a second generally triangular removable floor section 43. Two pipe tong latch and back-up posts 44 are mounted on the sta tionary portion of the floor adjaceint the rotary table. The rotary table is located on a sled 45 which also carries a spider base 46. The sled is retractable transversely of the vessel into a tunnel 47 which extends inwardly of the rig from the port edge of the floor.

The portion of the floor aft of the in-use position of sled 45 (the position shown in FIG. 2) is defined by two doors 48 and 49 which are hinged to the stationary portions of the floor along collinear, fore-and-aft hinged axes 50. When closed, the doors span opening 29' in the rig foundation.

The surface of floor structure 15 is defined by planking (see FIG. 2) which is laid over floor substructure 52 (see FIG. 3) as well as over removable sections 41 and 43 and over doors 48 and 49. The floor substructure includes frameworks 41 and 43 for floor removable sections 41 and 43, and frameworks 48' and 49' for doors 48 and 49. Those elements of FIG. 3 in which dash-dot-dash lines are used are movable relative to the remaining elements of the floor substructure; a comparison of FIGS. 2 and 3 will show the correspondence between the movable portions of the rig floor and foundation opening 29.

FIG. 3 also illustrates that the floor substructure defines a thwartships passage 53 for sled 45, such passage being covered by raised planking 54 to define tunnel 47 as shown in FIG. 7. The floor substructure is defined predominantly by thwartship channels and I-beams 55; it also includes a fore-and-aft channel 56 extending adjacent the starboard side of door frameworks 48' and 49' (see FIGS. 3 and 4).

As best shown in FIGS. 3, 4, and 5, framework 48' for door 48 includes a thwartship I-beam 58 adjacent the rotary table and a thwartships channel 59, the flanges of which face forward, located along the aft edge of the framework. Framework 49' for door 49 includes, all as thwartships elements, a forward channel 60 which has its flanges facing aft, and two I- beams 61. The flanges of each of elements 58-61 are cut away at the starboard ends of the elements, and the webs of these elements at their starboard ends each journal a corresponding hinge pin 62 (elements 59 and 60 cooperate with a common hinge pin as shown in FIG. 4) which are mounted coaxially of each other in vertical support lugs 63 extending toward the vessel centerline from channel 56 of floor substructure 52. In this manner the doors are mounted to the stationary portion of the drilling rig floor for hingable movement relative to the stationary portion of the floor about a foreand-aft axis lying essentially in the plane of the rig floor.

Hinge pins 62 are disposed outboard, and to starboard of foundation girder 30 which lies along the starboard side of space 29; each door framework includes a foreand-aft structural member 64 which engages the top of this girder when the door is closed (see FIG. 5). Three extensible, double-acting hydraulic rams 65 are pivotally coupled between girder 30 and framework 49' outboard of member 64; two extensible double-acting rams are similarly coupled to framework 48'. The rams are connected to a suitable source (not shown) of hydraulic power. The rams coupled to door 48 are operable independently of the rams coupled to door 49.

The unhinged ends of doors 48 and 49 rest upon girder 30 along the port edge of space 29 when the doors are closed. Thus, when the doors are closed, hinge pins 62 are essentially unloaded even though the doors may be supporting large loads.

The incorporation of doors 48 and 49 in the floor of drilling rig 14 enables the convenient provision of an access passage through the floor from the storage position of BOP stack 19 to the in-use position of the rotary table. As noted above, however, the BOP stack must be lowered through the center of well 13. Therefore, it is necessary that the access passage for the BOP stack be extended forward in the drilling rig, beyond the forward extent of door 48, at the time it is desired to lower the BOP stack to the submerged wellhead, so that the BOP stack may be centered over the vessel center well. Such extension of the BOP stack access passage is accomplished by fully retracting rotary table sled 45 into tunnel 47 and by removing floor sections 41 and 43. Since floor sections 41 and 43 are relatively small and light in weight, the removal of these sections from the stationary portion of the rig floor can be accomplished rapidly and easily through the use of cables extended from air tuggers 66 (see FIG. 2) located at various positions on the rig floor around the boundaries of the access passage. Metal floor plates 67 associated with rathhole 42 are also removed readily by the use of the air tuggers.

Sled 45 (see FIGS. 8 and 9) includes an elongated bed 6 70 having a width sized to fit within the width of passage 53 and of tunnel 47 (see FIG. 7). The bed is defined by a pair of parallel beams 71 which have fiat bottom surfaces 72. Surfaces 72 are arranged for sliding along the greased upper surfaces of the flanges of a pair of thwart ships beams 73 which form a portion of foundation 16 (see FIG. 6) between port arch 24 and port box beam 28; similar beams 74 are included in the foundation in conjunction with box beams 28'. The upper surfaces of box beams 28, 28, and arch 24, and of beams 73 and 74 are coplanar and define slide ways for sled 45 along the bottom of tunnel 47 and passage 53, as well as along a recess 75 in the foundation along the starboard side of passage 29 in alignment with passage 53.

An electric motor 77 is mounted to the port end of the sled bed (see FIG. 8) and has an output shaft 78 which is coupled via a clutch 79 to the drive shaft 80 of rotary table 18 which is also mounted to the sled bed to span the space between beams 71. The rotary table is also supported by a pair of beams 81 which are permanently connected between beams 71. A cover plate 82 is provided over the motor flush with the top of the rotary table. Power is supplied to the motor, at any position of the sled in the rig floor, via a self-reeling power cable (not shown) extending from the port end of the sled.

Spider base 46 is mounted to the sled bed adjacent the rotary table on the side of the table opposite from motor 77. The structure of the spider base includes side walls 84 parallel to beams 71, spaced transverse beams 85 which are removably connected between beams 71, and a pair of top cover doors 86 which are hinged to side walls 84 by way of hinge pins 87. The cover doors are cooperatively recessed to define a circular opening through the sled when the doors are closed as shown in FIG. 9.

The starboard ends of sled beams 71 support an auxiliary work platform 89 which is comprised only of side Walls 90 and a pair of cover doors 91 each of which is hinged to a respective side wall 90 for rotation about a hinge axis 92 parallel to the length of the sled. Doors 91 are not recessed as are doors 86. When doors 91 are open, the starboard end of the sled defines a U-shaped recess which opens away from the rotary table. This recess can be extended to the rotary table by opening spider base doors 86 and by removing beams 85 of the spider base; this construction makes it very easy to quickly outfit the drilling rig for passage of a running tool, for example, through the floor and downwardly of the vessel.

The vertical extent of the auxiliary work platform above beams 71 of the sled bed is less than the vertical extent above these beams of the spider base and the rotary table. Accordingly, when the sled is disposed to place the sled in its most starboardward position (see FIG. 2), the auxiliary work platform is positioned under the floor planking which covers recess 75.

When the sled is in its most extended position (shown in FIG. 2), the sled is supported on box beams 28 and 28'. The sled, however, may be fully retracted into tunnel 47 from between these box beams. Since it is contemplated that vessel 10 may be pitching or rolling when the sled is moved, the center of gravity (represented in FIG. 8 by line 94) of the sled assembly is located to port of the axis 95 of rotation of the rotary table. Thus, as the sled is extended from its retracted position, the starboard ends of beams 71 engage box beam 28 before the sled center of gravity passes beyond box beam 28. The sled, therefore, cannot tip into the space provided between box beams 28 and 28.

Undesired tipping of the sled about box beam 28 is further prevented by registry of ribs 96, extending outwardly of beams 71 adjacent the port end of the sled (see FIG. 8), under cooperating flanges 97 (FIG. 13) extended inwardly of passage 53 from those of foundation girders 31 which define the sides of passage 53. The sled is guided linearly during its movement in the drilling rig by guide members 98 (FIG. 13) which cooperate with the inner sides of sled beams 71.

FIGS. 9 and 11 illustrate a locking mechanism 100 for securing sled 45 to the portion of foundation 16 which lies to starboard of space 29. A pair of spaced, vertical guide plates 101 are mounted to the upper surface of box beam 28' centrally of recess 75 to extend athwartships of the vessel. These guide plates cooperate with the opposing surfaces of sled bed beams 71 and are toed inwardly, as at 102, toward each other adjacent passage 29 to assure proper alignment of the sled with recess 75 should the sled be slightly skew to the recess as it approaches the recess from the tunnel. A latching pin 103 is journalled in each guide plate (see FIG. 11) for reciprocation fore-and-aft of the vessel upon operation of a toggle linkage 104. The toggle linkage includes a pair of links 105 each of which is pivoted between a corresponding latching pin and a bellcrank lever 106. The bellcrank lever is secured to a shaft 107 which i rotatably mounted to the foundation and which extends parallel to the foundation along the length of recess 75. The shaft extends between a pair of stops 108 which are fixed to the foundation to define the starboard limit of travel of the sled. The locking mechanism is operated by inserting a suitable handle (not shown) through a slot 109 (see FIG. 2) in the rig floor planking into engagement with the starboard end of shaft 107, and by moving the handle in such direction as to cause the latching pins either to extend from or to retract into guide plates 101.

The latching pins of locking mechanism 100 cooperate with apertures 110 and 111 formed in the inner (i.e., the opposing) faces of beams 71 of the sled bed (see FIG. 8). Apertures 110 are used in cooperation with the latching pins to secure the sled in such a position that spider base 46 is positioned over the center of well 13; in this position of the sled, the sled is partially retracted from its most extended position. Apertures 111 and the latching pins cooperate to secure the sled in its most extended position, as shown in FIG. 2, so that rotary table 18 is centered over the vessel center well.

The locking mechanism is particularly advantageous as a safety feature in the structure of rig fioor 15. As noted above, the rig floor is located high above the main deck of the vessel. If the vessel should be rolling to any appreciable extent, the sled will be subjected to thwartship accelerations and may tend to shift transversely of the rig floor while personnel are working on the rig floor and the sled. The locking mechanism secures the sled in those positions in which it is most frequently disposed so the sled cannot unexpectedly move from such position. Also, the latching mechanism holds the sled down against the foundation and prevents the sled from being lifted by drill pipe caught either in a spider or the rotary table.

FIGS. and 12 illustrate a drive mechanism 115 for powered movement of sled 45 transversely of the rig floor. A sled drive chain 116 (represented by a dashed line in FIG. 12) is secured at one end of its length to a lug 117 which depends from the center lower portion of the sled at the port end of the sled (see FIG. 12). The chain extends around an idler sprocket 118 which is rotatably mounted to the foundation between sled rail beams 73 just inboard of port arch 24. From the idler sprocket the chain extends to starboard centrally between the sled rail beams over an adjustable tensioning sprocket 119 to around a drive sprocket 120; the drive sprocket is rotatably mounted to the rig floor foundation outboard of box beam 28 centrally between the sled rail beams. Chain 116 extends to port from the drive sprocket back to lug 117 of the sled bed.

The chain drive sprocket is secured to a shaft 122 which is journalled to the foundation, as at 123, and which eX- tends parallel to box beam 28. The shaft is connected to the output shaft 124 of a reversible sled drive motor 125 mounted on a support platform 126 secured to th box beam. Motor may be a pneumatic motor or an electric motor, but a hydraulic motor is preferred in combination with a reduction gear system (not shown). Operation of the motor causes the sled to be driven linearly transversely of the rig floor between the position of the sled shown in FIG. 2 and a position in which the sled is fully retracted into tunnel 47 and engages port sled stops 128 (see FIG. 12) secured to rail beams 73 adjacent port foundation arch 24.

From the foregoing description, it is apparent that this invention provides a rig floor structure which enables the construction of economic drilling vessels capable of drilling submarine oil wells of essentially unlimited diameter. The invention makes it possible to locate the drilling rig floor sufficiently close to the vessel main deck that a safe margin of stability is assured for the vessel, yet the vessel is still given the capacity to drill wells of large diameter. Moreover, the above-described features of the invention make is possible to drill a well with greater efficiency than has heretofore been possible since valuable time is not lost in manually dismantling the rig floor structure to move the rotary table or to move a BOP stack into position over the vessel center well.

What is claimed is:

1. A drilling rig including a floor and a rotary table mounted in the floor at a normal operative position centrally of the side edges of the floor, and characterized in that the floor includes a major stationary portion and door means hinged to the stationary portion, the door means extending from the rotary table normal position to a side edge of the floor, power means connected to the door means for hingably moving the door means relative to the floor stationary portion to provide an access passage from the floor side edge to the normal position of the rotary table, and means for moving the rotary table from the normal position thereof to provide an extension of the access pasage to centrally of the floor.

2. A drilling rig according to claim 1 including a truss-like foundation supporting the rig floor at an elevated location above a supporting base, the foundation defining a space in the upper portion thereof below the floor access passage and the extension thereof, the space under the floor having dimensions in directions parallel to the floor at least as great as those of the extended passage in corresponding directions, the space extending to and through the side edge of the foundation corresponding to said side edge of the floor.

3. A drilling rig according to claim 2 wherein the means for moving the rotary table includes drive means coupled between the foundation and the rotary table operable for moving the table in the plane of the floor into and out of the normal operative position thereof.

4. A drilling rig according to claim 3 including guide means for guiding the rotary table for movement thereof transversely of the elongate extent of the access passage relative to the rig floor.

5. A drilling rig according to claim 4 wherein the guide means comprises a tunnel in the rig floor into which the rotary table is movable in response to operation of the drive means.

6. A drilling rig according to claim 5 including an elongate sled to which the rotary table is mounted and to which the drive means is connected, the sled having a length adequate to span the space defined by the foundation.

7. A drilling rig according to claim 5 including a spider base mounted to the sled, the sled having a length adequate to span said foundation space when either the rotary table or the spider base is disposed centrally of the side edges of the floor.

8. A drilling rig according to claim 7 wherein the spider base and the sled are constructed for defining an opening through the sled from the end of the sled disposed most outwardly of the tunnel in the normal operatlve position of the rotary table to the rotary table.

9. A drilling rig according to claim 6 including a drive motor for the rotary table mounted to the sled.

10. A drilling rig according to claim 6 including latch means operable for securing the sled in at least one selected position relative to the rig floor.

11. A drilling rig according to claim 1 including selectively operable means for securing the rotary table in said normal operative position.

12. A drilling rig according to claim 2 including hinge means connecting the door means to the floor stationary portion, and wherein the door means and the foundation are cooperatively configured and arranged so that the hinge means are essentially unloaded when the door means is closed relative to the floor.

13. A drilling rig according to claim 1 wherein the door means comprises a plurality of door units in the rig floor.

14. A drilling rig according to claim 13 wherein the power means comprises means for moving each door unit hingably relative to the floor stationary portion independently of the other door units.

15. A drilling rig according to claim 1 wherein the drilling rig is disposed on a floating drilling vessel at an elevated location over a center Well formed through the vessel, and the normal operative position of the rotary table is centrally over the vessel center well.

16. In an installation for drilling submarine wells and the like including a drilling rig floor elevated above a floating supporting structure, a rotary table disposed in the rig floor and having a normal operating position centrally of the floor, and means mounting the rotary table in the floor for movement into and out of the normal operating position thereof, the improvement comprising selectively operable drive means continuously and positively coupled to the rotary table and operable for moving the table into and out of said position.

17. Apparatus according to claim 16 including a support to which the rotary table is mounted, a tunnel defined in the rig floor, and guide means cooperating with the support for guiding the support into and out of the tunnel during operation of the drive means.

18. Apparatus according to claim 17 including a drive motor for the rotary table mounted to the support,

19. Apparatus according to claim 17 including a spider base mounted to the support.

20. In a floating drilling vessel having a drilling rig floor fixedly elevated above and disposed substantially parallel to a main deck of the vessel over a center Well through the vessel, a rotary table mounted in the rig floor and having a normal operating position over the Well, and in which the rig floor has a stationary portion and includes a second portion thereof extending at least from the normal position of the rotary table to a side edge of the floor which is effectively removable from the floor stationary portion, and a foundation supporting the rig floor above the vessel main deck, the improvement comprising a permanent opening defined by the foundation in the portion of the foundation supporting said side edge of the rig floor, said opening being aligned with the second portion of the floor.

21. Apparatus according to claim 20 wherein said opening extends within the foundation vertically through the foundation and horizontally of the foundation longitudinally and transversely of the vessel amounts substantially equal to the corresponding extents of the floor second portion.

22. Apparatus according to claim 20 including means for storing a blowout preventer stack on the vessel main deck laterally of the rig floor adjacent the foundation opening.

References Cited UNITED STATES PATENTS 1,681,533 8/1928 Giliasso 175-8 2,515,540 7/1950 Willey 175-9 X 2,889,795 6/1959 Parks l5 X 2,981,346 4/1961 Baur -5 2,999,549 9/1961 Stratton l755 3,001,594 9/1961 Suderow 175-9 3,043,255 7/1962 Bauer 175-7 X 3,189,093 6/1965 De Vries 166-.5

NILE C. BYERS, 1a., Primary Examiner 

